Method and apparatus for managing moisture buildup in pressurised breathing systems

ABSTRACT

A vent assembly is configured to discharge gas washout from a patient interface that is configured to receive a pressurized flow of breathable gas from a positive airway pressure device. The vent assembly includes a vent base configured to be attached to the patient interface and comprising a plurality of coplanar openings and a hydrophilic material positioned adjacent to the coplanar openings. The hydrophilic material is configured to wick water near the plurality of coplanar openings and/or capture moisture from a gas washout flow adjacent to the plurality of coplanar openings. In addition, the hydrophilic material is configured to release the accumulated moisture and/or water to the pressurized flow of breathable gas for breathing by the patient when the patient inhales.

CROSS REFERENCE TO PRIORITY APPLICATION

This application is a continuation of U.S. application Ser. No.16/918,432, filed Jul. 1, 2020, now allowed, which is a continuation ofU.S. application Ser. No. 15/629,115, filed Jun. 21, 2017, abandoned,which is a continuation of U.S. application Ser. No. 11/988,541, filedJan. 10, 2008, now U.S. Pat. No. 9,717,870, which is the U.S. nationalphase of International Application No. PCT/AU2006/001081, filed 31 Jul.2006, which designated the U.S. and claims the benefit of U.S.Provisional Application No. 60/703,456, filed Jul. 29, 2005, each ofwhich is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

The present invention relates to a method and apparatus for managingmoisture buildup in humid pressurized breathing systems subject tohumidity consideration, etc., e.g., breathable gas supply apparatus foruse in Continuous Positive Airway Pressure (CPAP) treatment ofObstructive Sleep Apnea (OSA) and various other respiratory disorders,and diseases. In one example, a respiratory mask is provided with a ventaffording reduced noise and/or improved vent flow under humidified gasflow conditions.

CPAP treatment devices typically provide a gas flow generator fordelivering pressurized breathable gas, usually air, to a patient'sairway using a conduit and mask. In many such devices, the gas flowgenerator is combined with a humidifier to deliver pressurizedhumidified gas. The pressurized and optionally humidified gas acts as apneumatic splint for the patient's airway, preventing airway collapse,especially during the inspiratory phase of respiration. The humidifiedgas minimizes drying of the nasal mucosa and increases patient comfort.Many standard vents for respiratory masks have adverse reduced flow whenused with humidified air, either due to the build up of moisture at theentry to the vent or the blocking of the small gas pathways through thevent. For example, the vent manufactured by Gottlieb Weinmann Gerate FurMedizin Und Arbeitsschutz GmbH & Co. is known to reduce the vent flowwhen used with humidified gas. See European Patent No. 0 697 225 A2 toGottlieb et al. The blockage of the small gas pathways through the ventis a particular problem at low pressures such as 4 cm of H₂O or below.Blockage may occur because pressure is insufficient to keep the pathwaysclear. In this event, the minimum flow condition for safe CO₂ washoutmay be compromised, especially at the low end of the pressure treatmentrange.

Further, standard vents, including low noise vents, sometimes encounterobstruction of the gas vent pathway following washing of the mask orvent. Moisture can be retained around the entry or the exit of the ventor within the internal pathways of the vent. At low pressuresimmediately following a washing of the mask or vent, considerable timemay elapse before the moisture is cleared. If the mask is in use whilethe vent is being cleared, the system has reduced airflow leading toundesirable retention of CO₂ within the mask.

BRIEF SUMMARY OF THE INVENTION

One aspect of the invention is directed to providing a super quiet ventfor use in medical masks, e.g., for sleep apnea treatment. The vent canbe in the form of a diffuser vent that can maintain flow even in wetand/or humid conditions.

In another aspect of the present invention, a vent gas flow path isconstructed to provide sufficient venting under humidified gas flowconditions, any obstructions in the vent due to moisture in theoutflowing gas or remaining after washing being minimized or eliminated.

In another aspect of the present invention, the vent is constructed todisplace or reduce the moisture from the venting pathway. This may beaccomplished by preventing moisture from entering the vent pathway orfacilitating movement of the moisture away from the vent pathway.

It will be appreciated that in many aspects of the present invention,the vent configuration may be disposed or created within the mask shellor maybe disposed in additional piping extending from the mask, in bothcases enabling the outflow of gas, e.g., from the inner cavity withinthe mask, to atmosphere.

In one example of the present invention, there is provided a respiratorymask comprising a mask body having a patient interface at least in partdefining a breathing cavity, and a gas washout vent in communicationwith the cavity and including a porous portion, the porous portionincluding a hydrophobic or hydrophilic material. The porous portion maytake the form of a porous insert, a porous disk, a plastic portion, aporous sintered plastic, a membrane (with one or more holes), a textileand/or a plastic lined with a textile. The porous portion may be made ofplastic material, e.g., polyethylene and/or polypropylene, and it mayhave a granular structure or a surface structure (e.g., smooth, rough,one or more sides). The porosity may be in the range of about 120-220μm. Depending on the thickness the porous portion may also serve as afilter. 120-220 μm is the ideal range as a balance between having thelowest noise production, adequate resistance to blockage with humidity,and an appropriate size to be included in a mask system. For ideal noisethe porosity should be as fine as possible (<120 μm). For idealresistance to blockage the porosity should be as coarse as possible(>220 μm). A finer porosity vent however requires a much larger surfacearea to provide sufficient vent flow and a size limit therefore existsas to how low the porosity can be depending on the amount of spaceprovided for the vent in the mask design. To this end, the greatestsurface area available is the entire surface of the mask frame, and inthe extreme a mask frame could be made entirely of material that hassuper fine porosity, implementing the finest porosity whilst stillaffording sufficient vent flow.

In a further embodiment, a respiratory mask comprises a mask body havinga patient interface at least in part defining a breathing cavity; and agas washout vent in communication with the cavity and including atextile material on one side of the vent for wicking away moisture fromthe vent.

In a further embodiment, a respiratory mask comprises a patientinterface defining an opening communicating between a breathing cavityand an exterior of the patient interface, and a moisture retentionchannel formed adjacent the opening.

In a further embodiment, a respiratory mask comprises a patientinterface defining an opening in communication between a breathingcavity and an exterior of the patient interface, a port in communicationwith the breathing cavity, wherein the port has at least one portionformed of or treated with a hydrophilic and/or hydrophobic material.

The vent or port may include hydrophobic and/or hydrophilic materialsper se, or they may be treated with such. Alternatively, the vent orport or mask generally may simply be made of materials that simulate orhave hydrophilic and/or hydrophobic properties.

According to yet another embodiment, there is provided a method formanaging moisture and/or humidity in a pressurized breathing systemcomprising at least a selected portion of the mask manufactured from amaterial suited to manage moisture and/or humidity.

According to yet another embodiment there is provided a vent assemblyincluding porous material having different porosities in differentregions.

These and other aspects will be described in or apparent from thefollowing detailed description of preferred or exemplary embodiments.

In another embodiment a variable vent is provided and includes a closuremounted on at least one hydrophilic expansion member. When humid aircondenses in the vent and/or on the expansion member, at least some ofthe condensation is absorbed by the expansion member causing it toexpand. Expansion of the expansion member configures the closure in anopen configuration whereby air may pass more easily through the vent.The closure may be made from a porous material or a non-porous materialhaving a hole(s) therethrough.

In a further embodiment, a conical hole venting arrangement is provided.A porous plug is positionable within the conical hole (or may beintegrally formed therein), and when so arranged, a flange of the plugis disposed on an outside surface of the frame. The volume of theconical plug is greater than it would otherwise be if a cylindrical plugwere provided (i.e. one with a diameter corresponding to the small endof the conical plug) and thus advantageously is able to absorb moremoisture.

In one alternative embodiment the porous plug includes a core regionhaving a lower level of porosity and a surrounding infill region (ofsubstantially trapezoidal or triangular cross-section) having a higherlevel of porosity. This arrangement causes moisture absorbed by the coreregion to wick outwardly and upwardly to allow air to pass through thevent more freely.

In another embodiment the porous plug includes a number of poroussubstrates disposed transversly across the hole, wherein the material ofadjacent substrates have a decreasing level of porosity towards theflange region of the plug. In one embodiment between two and five poroussubstrates are provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a CPAP treatment device in the form of arespiratory mask and illustrating a vent constructed in accordance witha preferred embodiment of the present invention;

FIG. 2 is a view similar to FIG. 1 illustrating a different preferredconfiguration of mask and vent;

FIGS. 3 and 4 are partial cross-sectional views of a vent assemblyaccording to different embodiments of the present invention;

FIG. 5 is a fragmentary perspective view illustrating a mask having aremovable vent;

FIGS. 5 a and 5 b illustrate graphically the difference of howhydrophilic and hydrophobic materials interact with water, where thesize of the orifice (that a droplet resides in) approaches the size ofthe droplet;

FIGS. 5 c through 5 f are partial cross-sectional views of ventassemblies according to embodiments of the present invention;

FIGS. 6 a through 6 c illustrate various embodiments of vent materialwith variable porosity;

FIG. 7 a is a fragmentary cross-sectional view of a vent channel forremoving moisture prior to the gas flow encountering the vent;

FIG. 7 b is a view similar to FIG. 7 a illustrating a vent channeladjacent the exit of the vent;

FIG. 8 a is an enlarged fragmentary view of a vent in a respiratory maskaccording to a further embodiment of the present invention;

FIG. 8 b shows side-by-side cross-sectional comparative views of ventpathways with smooth and roughened surfaces, respectively;

FIG. 8 c graphically illustrates roughness measurement of a vent orificeaccording to an embodiment of the present invention;

FIGS. 9 a-9 c are schematic illustrations of further vent arrangementshereof;

FIGS. 10 and 11 are comparative graphs of flow rate versus pressure,illustrating non-humidified vent flow versus vent flow withhumidification; and

FIG. 12 is a comparative graph of the decrease in vent flow rate versuspressure for a prior art vent and a vent hereof.

FIGS. 13 a and 13 b show schematic side views of a variable ventaccording to a further embodiment of the present invention;

FIG. 14 is a schematic side view of a conical hole venting arrangementaccording to another embodiment of the present invention, including aporous plug.

FIG. 15 is a schematic side view of a conical hole venting arrangementaccording to one embodiment of the present invention, including a plughaving a core region of a lower level of porosity and a surroundinginfill region having a higher level of porosity.

FIG. 16 is a schematic side view of a conical hole venting arrangementaccording to another embodiment of the present invention, including aplug having a number of porous substrates disposed transversely acrossthe plug, adjacent substrates decreasing in porosity towards an outersubstrate.

FIG. 17 is a schematic view of an exemplary mask.

DETAILED DESCRIPTION OF EMBODIMENTS/EXAMPLES

FIG. 1 illustrates a breathing system in the form of a patientinterface, e.g., a nasal respiratory mask 10, according to a firstembodiment of the invention. Mask 10 includes a rigid plastic mask shell12 that has a peripheral flange 14 for mounting a cushion 11 to theshell 12 (see FIG. 17 ). The cushion 11 abuts the wearer's face in useand is well known in the art. The flange 14 includes slots 15 for theconnection of mask restraining straps (not shown) that extend around thehead of the wearer to maintain the mask 10 adjacent the wearer's face.The straps are also known in the art. The shell 12 also includes an arm16 which terminates in a fitting 18 adapted to connect to a foreheadsupport (not shown), which is also known in the art.

The mask shell 12 includes a breathable gas inlet 20, e.g., in the formof a swivel elbow that is rotatably mounted to the shell 12. The inlet20 has a first end 22 adapted for connection with a breathable gassupply conduit (not shown) coupled to a gas generator for supplying gasunder pressure. Inlet 20 has a second end 24, which is adapted toconnect to and communicate the supplied pressurized gas to the interiorof the shell 12 for subsequent communication with the wearer's airway.Mask 10 also includes a gas washout vent including an opening 26 in theshell 12 across which extends porous portion in the form of a thin airpermeable membrane 28, e.g., in the form of a porous disk or insert.Alternatively, the porous portion may take the form of a plasticportion, a porous sintered plastic, a textile and/or a plastic linedwith a textile. The porous portion may be made of plastic material,e.g., polyethylene and/or polypropylene), and it may have a granularstructure or a surface structure (e.g., smooth, rough, etc., on one ormore surfaces or sides), and the porosity may be in the range of 120-220μm. Depending on the thickness the porous portion may also serve as afilter.

FIG. 2 discloses a similar nasal respiratory mask 40, wherein likereference numerals are used to describe like parts as in the firstembodiment of FIG. 1 . Thus, the mask 40 has a shell 12 with a gas inlet20. Instead of slots 15 of the embodiment of FIG. 1 , the mask shellincludes openings 42 forming part of a bracket 43, which is adapted tosnap engage with connection fittings (not shown) provided on the end ofmask restraining straps (also not shown). Instead of the arm 16 andfitting 18, the mask 40 includes an adjustable forehead supportmechanism, indicated generally by the reference numeral 44. As in FIG. 1, mask 40 also includes a vent including an opening 26 formed in the gasinlet across which extends a thin permeable membrane 28. While these andother forms of masks are well known, the two forms specificallydisclosed herein are representative of the various known forms of masksand the washout vent described below may be utilized in any one or moreof those or other known masks.

Referring to FIG. 3 , there is illustrated an example of a washout vent48 according to an aspect of the present invention which includes amembrane 50 interposed between an outer mask element 52 and an innermask element 54. The membrane 50 is essentially clamped between the twoelements. The elements 52 and 54 have registering openings 56 and 58 andthe membrane 50 spans across the registering openings 56 and 58. Thisconstitutes only one example of various ways in which the membranedescribed in detail below may be mounted to the mask.

In FIG. 4 , there is illustrated another way of mounting the membrane50, similarly as in FIG. 3 , spanning the opening 56 of an outer maskelement 52. In this embodiment the membrane 50 is secured solely to theinner surface of the outer element 52 and is not clamped between the twoelements.

In FIG. 5 , the mask shell 12 has an opening 57, which receives aremovable holder 59. Holder 59 is preferably hollow and cylindrical andis releasably retained in the opening 57. The holder 59 includes aninterior membrane 60 spanning the orifice through holder 59. A grid 62is carried by holder 59 outwardly of the membrane 60 for protecting themembrane 60. It will be appreciated that the various membranes 25, 50and 60 disclosed in drawing FIGS. 1-5 are representative only of variousconfigurations and constructions of membranes for the vents forrespiratory masks in general and that the membranes as discussed in moredetail below have applicability to various other masks having vents forventing gas, particularly humidified gas, from respiratory masks.

Vent—Hydrophobic and/or Hydrophilic Materials

In an aspect of the present invention, the membranes illustrated inFIGS. 1-5 are preferably formed of or coated with a hydrophobicmaterial. Alternatively, the membranes could be treated with surfaceaffecting processes, e.g., nano treatment, coating, etc., similar toconcrete treatment. A surface formed of or otherwise having hydrophobicproperties of hydrophobic material repels moisture and water droplets.Consequently, if the vent surfaces or the entry to the vent surfaces areformed of hydrophobic material, the surfaces will resist moisture buildup through the gas pathways of the vent as well as at the entry to thevent. The surfaces repel the moisture or water droplets and encouragethe moisture or water droplets to run off the contacted hydrophobicsurfaces. The hydrophobic material may be porous portion in the form ofa porous plastic material and formed from such porous plastics aspolyethylene, polypropylene, PVDF and PTFE. These materials naturallyresist water entry into their pores. These materials are preferablysintered to form the porous construction. Alternatively, the materialmay be derived from a reticulated or cellular/matrix structure creatingone or a plurality of small tortuous paths for gas.

There are many different forms of vent constructions and configurations.In certain vent configurations, the formation of the membrane of, orproviding a vent coated with hydrophobic material, will cause a moisturedroplet to sit higher off the vent surface. This may increase itsproximity to the opposite vent surface tending to block the ventpathway. In those situations, vents formed of or coated with ahydrophilic material are beneficial. The formation of the vent orcoating or otherwise treating or providing the vent with a hydrophilicmaterial reduces the tendency of the moisture to remain within and blockthe vent pathway. As the moisture approaches the exit of the vent, thehydrophilic surfaces wick away the moisture thereby reducing blockage ofthe vent gas flow. Alternatively or in addition, the hydrophilic surfacesimply allows the air to pass because the droplet has a low profile.

For example, FIG. 5 a shows a vent hole 50.5 having a diameter definedby an inner surface that is formed or treated with a hydrophobicmaterial, while FIG. 5 b shows a similar vent hole 50.6 provided ortreated with a hydrophilic material. Each vent hole 50.5, 50.6 isapproximately the same size, yet the water droplet in FIG. 5 a tends tomore fully occlude the vent hole as compared to the relatively more openvent hole in FIG. 5 b.

Various combinations of materials may be used to achieve the desiredeffect. For example, as shown in FIG. 5 c , the vent hole 56.1 may havea cross-section having a composite or laminate construction, e.g.,including two or more layers, such as a hydrophilic layer 56.2 and ahydrophobic layer 56.3. FIG. 5 d shows a relatively thin porous portionhaving a thickness of around 1-2 mm, in the form of a membrane 50.1 thatis thinner than the adjacent wall/frame structure 52.1 supporting theporous portion. FIG. 5 e shows a relatively thick porous portion havinga thickness of 1 to 20 mm and preferably 3 to 7 mm. The relatively thickporous portion is in the form of a porous disk (e.g., a depth filter50.2—a filter that has some depth to it (not a thin filtrationmembrane)) that is thicker than the supporting frame/wall 52.2. FIG. 5 fis a cross-section of a porous portion in the form of a snap-fit plasticmember 50.3 that is removable/attachable to a frame 52.3.

Another use of hydrophilic material, aside from the collection orchanneling of moisture, is to prevent moisture from blocking and/oradversely affecting other parts or ports of the mask used to convey gas.For example, most masks include a pressure port or an O₂ therapy port onthe frame (e.g., frame 12 in FIG. 1 ) which can be fitted for formedwith a hydrophilic material to prevent fouling of the port. This aspectand other aspects of the invention may be applied to any fluid (e.g.,air) transmission orifice or orifices whereby control or management ofmoisture is desirable.

Porous Plastic Sintered Materials

As with hydrophobic materials, the hydrophilic material may comprise aporous plastic material, such as hydrophilic polyethylene manufacturedby Porex Corporation of Fairburn, Georgia. Other suitable material suchPorex Porous Plastic and Oriented Fiber hydrophilic products can bedesigned to wick moisture and water droplets at different rates. See,for example, U.S. Pat. No. 6,638,610, issued Oct. 28, 2003, incorporatedherein by reference. While “Porous Plastic” may be naturallyhydrophobic, such material can be made hydrophilic if treated, e.g.,with a surfactant.

When using the Porex hydrophilic products, such as Porex ProductXM1839PE (Polyethylene), the pore size may be 120-270 μm, preferably170-220 μm, and the product may have a 5-35 mm diameter (e.g., about 20mm) and a 1-10 mm thickness (e.g., about 5 mm). It has been found thatthese dimensions result in a balance of low noise and maintainingadequate flow even in humid conditions. The use of hydrophilic sinteredplastic vents affords efficient airflow for CO₂ removal whileeliminating much of the vent flow noise associated with traditionalventing methods. The vents are produced in plastic moldings preferablyusing a sintering process and may be molded into any geometry achievableby injection molding technology. The materials used in the mask and ventmay be co-moldable and thereby facilitate or eliminate assembly issues.The vent 26 may also be located in any pathway component of the mask 10,such as the frame 12, elbow 20, cushion clip, forehead support,anti-asphyxia valve, cushion 11 or swivel, or air supply or ventingpipes. See FIG. 17 . Further, the interface component, e.g., mask frame,can be manufactured from the stated materials, therefore providing anumber of utilities or functions for components, thus potentiallyreducing the number of parts, which can result in ease of use andreduced manufacturing costs. For example, the entire frame 12 of FIG. 1or the elbow 20 of FIG. 2 could be made of the stated materials.Moreover, the feature or component including the materials can be anadd-on, molded-on, retrofit or completely integral. The hydrophilicporous plastic, such as the Porex Porous Plastics noted above, isadvantageous in that it can be easily cleaned with a mildly abrasivecleanser to remove dirt, grease, smudges and the like. Heavy grease oroils may be removed with a solvent.

As illustrated in drawings FIGS. 1 and 2 , the gas, e.g., air, passesthrough the sintered plastic hydrophobic or hydrophilic material suchthat the pressure difference between the inside of the mask or otherpiping and the atmosphere drives the gas through the fine pores of thematerial itself into the atmosphere. This has the effect of exhaustingthe air to atmosphere in a highly diffuse manner. Forcing the gasthrough the tiny tortuous paths in the sintered plastic materialgenerates a high magnitude of viscous loss in the air. This causes theair to vent to atmosphere at very low velocity for a given bulk flowrate, and hence produces minimal noise. A generally higher surface areais required for vents of this type as compared with conventional ventingorifices. The required area will depend greatly upon the porosity andthickness of the material used for the vent. Note that porous materialshave been used previously for washout vents. See, for example, U.S. Pat.No. 6,581,594, as well as European Patent No. 0 697 225 A2 to Gottliebet al. This European patent discloses a vent formed from a poroussintered material. However, the porosity and thickness of the vent foruse in the present invention differs considerably from the Gottlieb etal. vent. Gottlieb et al. discloses a generally cylindrical insert,including a window, covered with a porous sintered material ofapproximately 3-4 mm thickness, but with a much finer porosity than setforth herein. The large pore size of the washout vent membranes hereinalso provide a flatter pressure flow curve, which is preferable toprovide more vent flow at low pressures and less vent flow at highpressures.

Variable Porosity

Referring now to FIGS. 6 a-6 c the vent membranes may be formed of ahydrophobic or hydrophilic material, which has variable porosity acrossthe thickness of the membrane. Variable porosity in these materials maybe achieved in the manufacturing process or by using a layer of materialhaving a variable porosity. For example, as illustrated in FIG. 6 a ,the hydrophobic or hydrophilic sintered porous plastic material formingthe membrane 50 may have a fine pore size present at the entry to thevent and a larger pore size at the exit of the vent. The direction ofthe gas flow venting through the membrane 50 is represented by the arrow70. In FIG. 6 a , the fine pore size is represented by the smallercircles 72 within the membrane adjacent the gas entry surface of themembrane in contrast to the larger pore size represented by the circles74 adjacent the opposite gas exit surface of the membrane. In FIG. 6 b ,the reverse configuration is illustrated. That is, the hydrophobic orhydrophilic sintered porous plastic material may have the coarse poresize 74 at the entry surface of the vent and the finer pore size at theexit surface of the vent. A particular advantage of the use of avariable porosity material is that it enables a surface which is lesslikely to be blocked by moisture to be presented to highly humidifiedgas at the entry of the vent and a surface that is less likely to beblocked by dirt to reside at the exit of the mask where it may come intocontact with dirt or grease.

Referring to FIG. 6 c , variable porosity of the membrane may beachieved by layering materials of different porosities. For example, asillustrated in FIG. 6 c , the entry to the vent membrane represented bythe small circles 72 may be formed of a hydrophobic or hydrophilicsintered plastic material having the fine pore size in a first layer 76on the entry side of the vent. An exit 78 formed of a hydrophobic orhydrophilic sintered plastic material having a coarse pore sizerepresented by the larger circles 74 may be provided on the oppositeside of the vent. Additionally, the interior layer may be formed ofhydrophobic material covering or partly covering a hydrophilic layerwhich is at the exterior of the mask. With this construction, surfacemoisture tends to run off the vent with the hydrophilic layerencouraging humidified gas to flow through the vent. Alternatively, thehydrophilic material may constitute an interior layer at the entry tothe vent, i.e., about the interior of the mask encouraging thehumidified gas to flow through the vent. The exterior layer constitutedby the hydrophobic material may encourage moisture, e.g., remnants ofmoisture from a prior washing of the vent, to run off the vent and maskand prevent blocking of the vent.

Moisture Collection Channel

Referring to FIG. 7 a , a layer 80 of either hydrophilic and/orhydrophobic porous material may be positioned prior to the gas entry tothe vent 82. This inhibits build up of moisture at the entry of thevent. In the case of hydrophobic material, the interior layer 80 mayonly be partial, e.g., donut shaped or annular, thus allowing humidifiedgas to pass unfiltered through an opening in the center of the layer, orother openings thereof, but still preventing the build up of moistureabout the entry to the vent. The vent 82 may be formed of conventionalvent material, such as sintered metal or may be formed of thehydrophobic or hydrophilic material. The material may also be structuredto increase the surface area within a smaller overall size vent.Increased surface area may be implemented using pleats, etc.

In FIG. 7 b , a layer 86 of hydrophilic or hydrophobic porous materialis positioned adjacent the exit side of the vent 88. In both cases usingthe hydrophobic or hydrophilic materials tends to flow moisture awayfrom the vent openings.

The embodiments of FIGS. 7 a and 7 b include a washout vent structuremounted on a selectively removable holder similar to that shown in FIG.5 . However, the vent could also be mounted directly on the frame (oralong another portion of the gas delivery path), e.g., as described inU.S. Pat. Nos. 6,561,190 and 6,561,191, incorporated herein by referencein its entirety).

Further, the embodiments of FIGS. 7 a and 7 b may include a moisturecollection area, e.g., in the form of a trough or channel that may beplaced in the vicinity of the opening of the frame. In the exampleillustrated, the trough is in front of the opening, but it could also bepositioned on the inside of the frame.

Roughened Surface

Referring to FIG. 8 a , there is illustrated a further form of ventdisclosed more particularly in U.S. Patent Application Ser. No.60/643,114, filed Jan. 12, 2005, incorporated herein by reference in itsentirety. As described and illustrated in that application one of thepreferred vents comprises a generally U-shaped passage 90. Vent 90 andoptionally the overall mask frame where the vent is situated may beformed of the porous, sintered plastic hydrophobic and/or hydrophilicmaterials described herein. The surfaces of the vent passage 90 may havea roughened finish. In FIG. 8 b , the left side of the drawing figureillustrates vent passages 92 which are continuous and smooth, albeit thewalls of the passages undulate. The masks are made of moldedpolycarbonate, and may even have a small degree of roughness. In theright side of FIG. 8 b , the walls of the passages 94 are illustrated ashaving highly roughened surfaces (e.g., like the roughened surfaceswhich are generated using rapid prototype components(Objet®/SLA)—component made from a rapid prototyping process usingstereolithography which deposits consecutive fine layers of plasticmaterial according to input from a 3-D CAD model. Roughened surfaces ofhydrophobic or hydrophilic material are particularly desirable as thevents produce reduced noise. The roughness can be quantified in terms ofthe ratio of the thickness of the roughened portion in relation to theoverall height (or diameter) (H) of the orifice, as shown in FIG. 8 c .The roughness (R) should be in the range of H/50<R<H/2, and preferablyH/10<R<H/5. Thus, if H is 0.7 mm, the roughness R will be between about0.07 mm and 0.14 mm. In the example of FIG. 8 c , an exemplary roughnessof H/20 is shown in one region and a preferred roughness of H/5 is shownin another region. The dimension is defined as the height differencebetween the trough and the apex of the asperity. Thus, by molding ventcomponents out of a plastic material, a roughened surface finish (likethat shown on the right side of FIG. 8 b ) can be utilized as a noisereduction mechanism, while the properties of the hydrophobic orhydrophilic materials assist in moisture management, e.g., to wickmoisture and/or to maintain the vent orifices open thereby minimizingrisk of blockage with moisture.

Membrane with Holes

Further, use of non-porous hydrophobic or hydrophilic material,specifically plastic, which contains a number of venting holes (e.g.,through holes) each having a diameter of up to 0.8 mm may be utilized.This provides a low noise solution, which will not significantly blockhumidified gas. Alternatively, the vent may be formed fromnon-hydrophilic or non-hydrophobic material and later coated withhydrophilic or hydrophobic material. The preferred arrangement issimilar to that described in the stainless steel embodiment of U.S. Pat.No. 6,581,594, where the holes are smaller than 0.2 mm in diameter. In afurther preferred embodiment (similar to the stainless steel embodimentprovided in U.S. Pat. No. 6,581,594), the vent has a thickness ofapproximately 0.45 mm and a number of holes, each hole having a diameterof approximately 0.1 mm. The total open area of such a stainless steelmembrane is approximately 5%. However, the vent geometry may take theform of any tapered or non-tapered vent geometry that is known in theart with a hydrophilic or hydrophobic coating enhancing the use of thevent with humidified air.

Wicking Textiles

In a further embodiment, a laminated textile may be used to provide thevent so that the vent has self-wicking capability. For example, in FIG.9 a , a plastic vent 100 containing small holes 102 may be provided as alow noise solution vent surrounded by a cotton based material 104 thathas a capillary action. Thus, the cotton material 104 surrounding thevent 100 wicks the water from the vent. The wicking action may be alonga direction D that is transverse to the axis of the holes 102.1, asshown in FIG. 9 c . and can be directed towards an adjacent membrane orpart of the same membrane. Alternatively and in FIG. 9 b , a textile110, such as cotton, may be applied as a protective layer in front ofthe vent 112. The protective layer captures the moisture and acts towick the moisture away from the vent, while the flow passes through theprotective layer and through the small holes in the low noise vent. Aswell as providing a mechanism for maintaining flow under humidifiedconditions, an extension of this mechanism is to wick the moisture awayto a membrane where it can be subsequently exposed to the breathing gasflow, therefore acting as a humidifier for the breathing gas.

Further, a heated textile or conductive yarn with a current supplied toit (e.g. SoftSwitch as disclosed by Canesis Ltd) can surround theplastic vent or each individual vent hole. The textile preventscondensation of the humidified gas due to the raised temperature of thevent surface. The heated textile may also continue into the air path,e.g., into the mask frame, to increase the exposed area and increasehumidity of the breathing gas and/or temperature, especially desirablein cooler climates.

Wicking can be accomplished using a yarn material stitched togetherclosely to allow moisture to capillate between yarns or it may also beat the fiber level, wherein each yarn is capable of capillary action.

The textile fabric that holds moisture can have a dual utility in thatthe trapped moisture may be rebreathed to assist with moisturizingand/or humidifying the breathing air.

Another way to control the flow through a porous vent underhumidification is to draw the moisture away from the vent area usingcapillary action as will now be described. A mask frame 140 includes avent assembly 142. The vent assembly 142 has a patient side 144 and anoutside 146. The frame 140 includes an orifice 141 having a generallyconical shape, with the narrow end of the vent on the patient side 144of the mask. This will allow more area for the moisture to move to whenabsorbed. Porous material 148 is arranged within the orifice 141 andextending to the outside of the frame. An additional porous layer 149would be on the outside of the frame. This extra area would act as asponge drawing water away from the vent and helping control the ventflow. See FIG. 14 .

Using various pore sizes throughout the vent, the path of the moisturecan be controlled. Moisture will more readily condensate onto/intomaterials with a larger surface area.

Another embodiment of the vent of FIG. 14 is shown in FIG. 15 . Thisembodiment involves a core 150 of less porous material surrounded by amore porous outer layer. The more porous area would act as a wick forthe moisture to move through. An outer layer on the mask would also berequired for moisture dissipation. See FIG. 15

Another embodiment of the above would have multiple layers 160 of porousmaterial that would absorb moisture at different rates. See FIG. 16 .Initial condensation will occur on the layer that is on the patient sideof the vent. The moisture will then be attracted into the layers aboveand out to the outer surface of the mask.

Comparative Graphs

Referring to FIG. 10 , there is illustrated a graph of flow rate throughthe vent versus pressure using a sintered polyethylene hydrophilic ventbefore and four hours after humidification. As illustrated in thisgraph, even with humidified air, the flow rate does not decreasesubstantially and decreases no more than 15% at any pressure. The flowrate is safe even at low pressures, with and without humidity.

In FIG. 11 there is a similar graph comparing vent flow beforehumidification and vent flow after four hours of humidification with asintered porous vent constructed in accordance with the GottliebEuropean patent previously identified. This graph illustrates very lowflow (potentially unsafe CO2 washout) even without humidity. Withhumidity, the flow is dangerously low.

In FIG. 12 , the graph indicates the percentage decrease in flow rate atvarious pressures for the Gottlieb sintered porous vent as compared witha sintered polyethylene hydrophilic vent hereof, the performance ofwhich is set forth in FIG. 10 . The graph of FIG. 12 demonstrates thedecrease in flow rate utilizing the hydrophilic vent structure of anembodiment of the present invention (designated “PE”) in comparison withthe Gottlieb vent designated “WM”. At the desirable low pressures, itwill be appreciated that the decrease in flow rate of the presentinvention is advantageously considerably less than the decrease in flowrate of the Gottlieb vent. The vent designated as “PE” provided adequateflow for CO₂ washout, even at lower treatment pressures—both without andwith humidity. Gottlieb (“WM”) flow falls to below safe levels whenhumidity is passed through the vent. This vent also takes a considerableamount of time to clear and recover from humidity blockage.

Protective Structure

As illustrated in FIG. 5 , an outer protective layer or plate 62 may beprovided outside the vent membrane 60 and may comprise a coarse mesh orbars which protects the membrane from damage from large contaminants andhandling. Alternatively, the protective plate or mesh may be eliminatedif the vent is recessed within the mask frame or within the removableholder 58.

End of Life Indicator

An end-of-life indicator may be mounted on or adjacent to the vent toalert the user to the need to replace the vent. The indicator mayprovide an indication of the elapsed time that the vent has been in use,blockage of the vent due to humidity or blockage of the vent due tocontamination or reduced vent flow rate. The indicator may be eithervisual or audible. For example, the indicator may include a watersoluble dye that gradually washes away, similar to wear indicatorsprovided in some tooth brushes.

Variable Venting

To compensate the hydrophilic nature of the porous vent, a variable ventcan be implemented to compensate the flow reduction.

In this form of the invention, a layer of porous material 130 is mountedon feet 132 in a slotted hole 134. The feet 132 are made of ahydrophilic material that expands when moist. This expansion lifts theporous material 130 out of the hole creating a vent in the gap betweenthe frame and vent. See FIG. 13 a . Crimping the edge of the hole couldreduces noise through variable vent.

As the humid air condenses in the vent, it will also be condensing inthe feet. In a preferred form the flow reduction in the vent equals theflow increase created by the expanding feet.

When the feet dry out (release moisture), they will shrink, reducingflow through the variable vent see FIG. 13 b . In a preferred form thereduction in flow of the variable vent equals the increase in flowthrough the porous vent as it dries out.

In another form the variable vent is used in conjunction with atraditional vent. Instead of a porous vent being attached to the feet, anonporous material is used. The flow increase of the variable ventcounteracts the flow decrease caused by humidification at thetraditional vent.

While the invention has been described in connection with what arepresently considered to be the most practical and preferred embodiments,it is to be understood that the invention is not to be limited to thedisclosed embodiments, but on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the invention. Also, the various embodiments described abovemay be implemented in conjunction with other embodiments, e.g., aspectsof one embodiment may be combined with aspects of another embodiment torealize yet other embodiments. In addition, while the invention hasparticular application to patients who suffer from OSA, it is to beappreciated that patients who suffer from other illnesses (e.g.,congestive heart failure, diabetes, morbid obesity, stroke, barriatricsurgery, etc.) can derive benefit from the above teachings. Moreover,the above teachings have applicability with patients and non-patientsalike in non-medical applications.

1. (canceled)
 2. A vent assembly configured to discharge gas washoutfrom a patient interface that is configured to receive a pressurizedflow of breathable gas from a positive airway pressure device, the ventassembly comprising: a vent base configured to be attached to thepatient interface and comprising a plurality of coplanar openings; and ahydrophilic material positioned adjacent to the coplanar openings,wherein the hydrophilic material is configured to wick water near theplurality of coplanar openings and/or capture moisture from a gaswashout flow adjacent to the plurality of coplanar openings, and whereinthe hydrophilic material is configured to release the accumulatedmoisture and/or water to the pressurized flow of breathable gas forbreathing by the patient when the patient inhales.
 3. The vent assemblyof claim 2, wherein the hydrophilic material is configured to wickmoisture away from the plurality of coplanar openings in a directionthat is transverse to a direction of airflow through the vent assembly.4. The vent assembly of claim 2, wherein the hydrophilic material isconfigured to be between a patient and the plurality of coplanaropenings in use.
 5. The vent assembly of claim 2, wherein thehydrophilic material is a textile.
 6. The vent assembly of claim 2,wherein the vent base is made of plastic.
 7. The vent assembly of claim2, wherein the hydrophilic material is positioned so that gas washoutflows through the hydrophilic material before flowing through theplurality of coplanar openings.
 8. The vent assembly of claim 2, whereinthe hydrophilic material is configured to be between a patient and theplurality of coplanar openings in use, wherein the hydrophilic materialis a textile, wherein the vent base is made of plastic, and wherein thehydrophilic material is positioned so that gas washout flows through thehydrophilic material before flowing through the plurality of coplanaropenings.
 9. A patient interface assembly configured to receive apressurized flow of breathable gas from a positive airway pressuredevice, the patient interface comprising: a cushion configured tosealingly engage a patient's face; a shell with an opening configured toreceive the pressurized flow of breathable gas and discharge gaswashout; and the vent assembly of claim 2, wherein the vent assembly isconfigured to be attached to the shell adjacent to the opening in theshell.
 10. The patient interface assembly of claim 9, wherein the ventassembly is removable from the shell.
 11. The patient interface assemblyof claim 9, further comprising an air delivery tube connector configuredto be attached to the shell.
 12. A vent assembly configured to dischargegas washout from a patient interface that is configured to receive apressurized flow of breathable gas from a positive airway pressuredevice by way of an air delivery tube, the vent assembly comprising: avent base configured to be attached to an air delivery tube connectorthat is configured to connect the air delivery tube to the patientinterface, the vent base comprising a plurality of coplanar airpassages; and a hydrophilic material positioned adjacent to the coplanarair passages so that gas washout flowing from the patient interfaceflows through the hydrophilic material and the plurality of coplanar airpassages, in use, wherein the hydrophilic material is configured to wickwater near the plurality of coplanar air passages and/or capturemoisture from the gas washout adjacent to the plurality of coplanar airpassages, and wherein the hydrophilic material is configured to releasethe accumulated moisture and/or water to the pressurized flow ofbreathable gas for breathing by the patient when the patient inhales.13. The vent assembly of claim 12, wherein the hydrophilic material ispositioned so that some of the gas washout bypasses the hydrophilicmaterial before flowing through the plurality of coplanar air passagesin use.
 14. The vent assembly of claim 12, wherein the hydrophilicmaterial is configured to wick moisture away from the plurality ofcoplanar air passages in a direction that is transverse to a directionof airflow through the vent assembly.
 15. The vent assembly of claim 12,wherein the hydrophilic material is configured to be between a patientand the plurality of coplanar air passages in use.
 16. The vent assemblyof claim 12, wherein the hydrophilic material is a textile.
 17. The ventassembly of claim 12, wherein the vent base is made of plastic.
 18. Thevent assembly of claim 12, wherein the hydrophilic material ispositioned so that gas washout flows through the hydrophilic materialbefore flowing through the plurality of coplanar air passages.
 19. Thevent assembly of claim 12, wherein the hydrophilic material isconfigured to be between a patient and the plurality of coplanar airpassages in use, wherein the hydrophilic material is a textile, whereinthe vent base is made of plastic, and wherein the hydrophilic materialis positioned so that gas washout flows through the hydrophilic materialbefore flowing through the plurality of coplanar air passages.
 20. Apatient interface assembly configured to receive a pressurized flow ofbreathable gas from a positive airway pressure device, the patientinterface comprising: a cushion configured to sealingly engage apatient's face; a shell with an opening configured to receive thepressurized flow of breathable gas and discharge gas washout; and thevent assembly of claim 12, wherein the vent assembly is configured to beattached to the shell adjacent to the opening in the shell.
 21. Thepatient interface assembly of claim 20, wherein the vent assembly isremovable from the shell.
 22. The patient interface assembly of claim20, further comprising an air delivery tube connector configured to beattached to the shell.